For the maintenance of a concrete construction, for example, it is known to persons skilled in the art to incorporate wireless IC tags, in which various information on a product, into a concrete construction and to manage the quality of the built concrete and the history of the construction by means of a management system employing such wireless IC tags in view of validating strength of the construction against earthquake, history of the construction and the like.
Besides, the product management for products being in any of liquid, viscous and semi-solid state in the manufacturing process, such as fresh concrete and thermoplastic resins, has been executed product by product by writing various data to wireless IC tags in advance, then embedding those IC tags into the product before having been cured to enclose them in the product, and reading said data from and/or writing new information to the wireless IC tags having been cured in the product by means of a radio communication.
In quality management of a concrete construction by means of wireless IC tags, when it is intended to obtain information written in the IC tag having been embedded in a concrete construction from the outside, it is required to search the location of the embedded wireless IC tags. For this purpose, it is known until today to use a searching apparatus, which is adapted to creep on the exterior surface of the concrete construction, and the preset part of which lights when it has come onto a point where a wireless IC tag has been embedded.
Further, as a searching system for product management, a method for detecting a distance and/or a position to an objective product to which an IC tag is stuck by transmitting radio waves to which the IC tag reacts from a reader, measuring the time until said radio waves has been returned, and detecting the distance and/or the position to the objective product based on the measured time (Patent Document 1) and another method for searching the source of sending information by receiving radio waves from an exterior information source as the preliminary searching by means of a directional antenna, calculating a reception level at that time, to store the level, carrying out the real searching again to compare the obtained reception level with the maximum value of the reception level at the preliminary searching and searching the source of sending information based on the detected maximum value (Patent Document 2) are known.